A seat belt system for restraining an occupant of a vehicle ordinarily includes seat belt webbing, a seat belt buckle, and a seat belt retractor. A locking tongue is connected to the webbing and is releasably lockable in the buckle when the webbing is extended around the vehicle occupant. The retractor includes a spool upon which the webbing is wound. The spool rotates in an unwinding direction when the vehicle occupant extracts the webbing from the retractor and moves the webbing toward the extended position in which the tongue is locked in the buckle. When the tongue is subsequently unlocked and released from the buckle, a rewind spring in the retractor rotates the spool in a winding direction to retract the webbing into the retractor.
When the vehicle experiences a collision, the vehicle decelerates and the vehicle occupant wearing the seat belt webbing moves forcefully against the webbing. The force which is then applied to the webbing by the vehicle occupant urges the webbing to move outward from the retractor. Therefore, a seat belt retractor typically includes an emergency locking mechanism which blocks unwinding rotation of the spool in response to sudden vehicle deceleration and/or sudden extracting movement of the webbing. The emergency locking mechanism thus prevents the webbing from moving outward from the retractor when the vehicle experiences a collision.
In some seat belt systems, the webbing is prevented from being further extracted from the retractor throughout the time that the webbing is secured around the vehicle occupant, i.e., the webbing is maintained in a cinched condition. The retractor in such a seat belt system includes an automatic locking mechanism. The automatic locking mechanism places the webbing in the cinched condition automatically when the webbing is extracted from the retractor in preparation for locking of the tongue in the buckle. The automatic locking mechanism maintains the webbing in the cinched condition as long the webbing remains extracted from the retractor, and releases the webbing from the cinched condition automatically when the webbing is subsequently retracted into the retractor after the tongue is unlocked from the buckle.